The present invention is concerned with production of electric power from a hydrogen fueled fuel cell supplied with hydrogen by an autothermal reforming process.
As is well known in the art, fuel cells generate electric current by the reaction of a fuel and oxidant brought into contact with a suitable electrolyte. Current is generated by a catalyzed chemical reaction on electrode surfaces which are maintained in contact with the electrolyte. Known types of fuel cells include a bipolar, phosphoric acid electrolyte cell which utilizes hydrogen as the fuel and the oxygen in air as the oxidant. One such phosphoric acid electrolyte cell available from Engelhard Corporation, the assignee of this application, utilizes a matrix type construction with bipolar stacking of hydrophobic electrodes, a concentrated phosphoric acid electrolyte and one or more platinum group metals as the electrode catalyst. Air or air with a circulating coolant may be used for heat and water removal from the cell, which is capable of utilizing impure hydrogen as the fuel. Other types of fuel cells which use hydrogen as the fuel are of course known, utilizing various cell constructions and various electrolytes such as aqueous potassium hydroxide, fused alkali carbonate, solid polymer electrolytes, etc. Various electrode catalysts, such as nickel, silver, base metal oxides and tungsten carbide are known as electrode catalysts. Although other fuels such hydrazine are known, hydrogen is the most commonly utilized fuel for fuel cells and reacts therein with oxygen introduced to the cell to yield water as a reaction by-product.
Fuel cells offer the possibility of significant advantages over other electrical power sources including low operating costs, modular construction which enables "tailor-made" sizing and siting of the units, and protection of the environment in view of the lack of significant noxious exhaust. A significant factor is the availability of a reliable and suitable source of hydrogen fuel. Hydrogen may be prepared from hydrocarbons by the partial oxidation of heavier hydrocarbons, such as fuel oil and coal, and by steam reforming of lighter hydrocarbons such as natural gas and naphthas. Processes to derive hydrogen from methanol or coal-derived hydrocarbons are also known. Generally, difficulties associated with the preparation of hydrogen from heavier feedstocks favor the use of light naphthas or natural gas as the hydrocarbon source. However, shortages of such feeds indicate the need for an economical method of generating a hydrogen-rich gas suitable for use as a fuel cell fuel from heavier feedstocks, such as normally liquid hydrocarbons. Further, most fuel cells are sensitive to hydrocarbons in the hydrogen fuel, so that it is necessary to eliminate or reduce to very low levels any residual hydrocarbons in the hydrogen fuel.
Steam reforming is a well known method for generating hydrogen from light hydrocarbon feeds and is carried out by supplying heat to a mixture of steam and a hydrocarbon feed while contacting the mixture with a suitable catalyst, usually nickel. However, steam reforming is generally limited to paraffinic naptha and lighter feeds which have been de-sulfurized and treated to remove nitrogen compounds, because of difficulties in attempting to steam reform heavier hydrocarbons and the poisoning of steam reforming catalysts by sulfur and nitrogen compounds.
Another known method of obtaining hydrogen from a hydrocarbon feed is the partial oxidation process in which the feed is introduced into an oxidation zone maintained in a fuel rich mode so that only a portion of the feed is oxidized. Steam may be injected into the partial oxidation reactor vessel to react with the feed and with products of the partial oxidation reaction. The process is not catalytic and requires high temperatures to carry the reactions to completion, resulting in a relatively high oxygen consumption. On the other hand, the partial oxidation process has the advantage that it is able to readily handle hydrocarbon liquids heavier than paraffinic naphthas and can even utilize coal as the source of the hydrocarbon feed.
Catalytic autothermal reforming of hydrocarbon liquids is also known in the art, as evidenced by a paper Catalytic Autothermal Reforming of Hydrocarbon Liquids by Maria Flytzani-Stephanopoulos and Gerald E. Voecks, presented at the American Institute of Chemical Engineers' 90th National Meeting, Houston, Texas, Apr. 5-9, 1981. Autothermal reforming is defined therein as the utilization of catalytic partial oxidation in the presence of added steam, which is said to increase the hydrogen yield because of simultaneous (with the catalytic partial oxidation) steam reforming being attained. Steam, air and a No. 2 fuel oil are injected through three different nickel particulate catalysts. The resulting product gases contained hydrogen and carbon oxides.
In Brennstoff-Chemie 46, No. 4, p. 23 (1965), a German publication, Von P. Schmulder describes a Badische Anilin and Soda Fabrik (BASF) process for autothermal reforming of gasoline utilizing a first, pelletized, platinum catalyst zone followed by a second, pelletized nickel catalyst zone. A portion of the product gas is recycled to the process.
Disclosure of the utilization of a noble metal catalyzed monolith to carry out a catalytic partial oxidation to convert more than half of the hydrocarbon feedstock upstream of a stream reforming zone is disclosed in an abstract entitled "Evaluation of Steam Reforming Catalyst for use in the Auto-Thermal Reforming of Hydrocarbon Feed Stocks" by R. M. Yarrington, I. R. Feins, and H. S. Hwang (National Fuel Cell Seminar, July 14-16, 1980, San Diego). The abstract noted the unique ability of rhodium to steam reform light olefins with little coke formation and noted that results were obtained for a series of platinum-rhodium catalysts with various ratios of platinum to total metal in which the total metal content was held constant.
U.S. Pat. No. 4,054,407, assigned to the assignee of this application, discloses two-stage catalytic oxidation using platinum group metal catalytic components dispersed on a monolithic body. At least the stoichiometric amount of air is supplied over the two stages and steam is not employed.
U.S. Pat. No. 3,481,722, assigned to the assignee of this application, discloses a two-stage process for steam reforming normally liquid hydrocarbons using a platinum group metal catalyst in the first stage. Steam and hydrogen, the latter of which may be obtained by partially cracking the hydrocarbon feed, are combined with the feed to the process.
The use of autothermal reforming as part of an integral fuel cell power plant to generate a hydrogen fuel from a hydrocarbon feed in order to supply a fuel cell, is shown in U.S. Pat. No. 3,976,507, issued Aug. 24, 1976 to D. P. Bloomfield. An autothermal reactor converts a hydrocarbon feed to supply a hydrogen-rich fuel to the anode gas space. The plant includes a compressor driven by exhaust gases from a catalytic burner to compress air supplied to the cathode gas space of a fuel cell stack. The cathode vent gas from the fuel cell is fed to the autothermal reactor and the anode vent gas is fed to the catalytic burner.
The present invention provides a highly efficient method for producing hydrogen-rich feeds for fuel cells from hydrocarbons which attains excellent yields in a relatively compact and simple apparatus.